1. Field of the Invention
The present invention relates to an electric motor controller that uses an electric motor to control driving of a driven body of a machine tool or industrial machinery and, in particular, to an electric motor controller having a function for simultaneously estimating inertia, friction, and a spring of the driven body.
2. Description of the Related Art
Learning magnitudes of inertia and friction of a driven body that is driven by an electric motor is not only important when determining machining conditions of a machine tool or the like but is also important for accurately controlling a drive shaft that drives the driven body.
For example, when determining acceleration and deceleration constants of a command as a machining condition, the magnitudes of inertia and friction must be accurately known in order to fully exploit the accelerating ability of the electric motor. In addition, regarding control, magnitudes of inertia and friction must be accurately known in order to calculate a gain that determines responsiveness of velocity control. Furthermore, robustness of a servo can be enhanced by constructing a disturbance observer using values of inertia and friction.
An electric motor controller comprising a function for simultaneously estimating inertia and friction is disclosed in Japanese Patent Application Laid-open No. 2011-072178. The controller specifically estimates controlled object parameters including nonlinear friction. The technique disclosed in Japanese Patent Application Laid-open No. 2011-072178 targets so-called one-inertial systems in which a controlled object is assumed as being a rigid body, and no disclosures are made in regards to controlled objects having spring characteristics. Many driven bodies in machine tools and industrial machinery cannot be treated as complete rigid bodies. Therefore, when a rigid body is assumed as a controlled object of estimation as is the case of the technique disclosed in Japanese Patent Application Laid-open No. 2011-072178, a problem arises in that the controlled object is limited to rigid bodies or estimation accuracy deteriorates when the controlled object is not a rigid body.
A technique in which a controlled object is assumed as being a resonance model and parameters of the controlled object are estimated by an iterative least square technique is disclosed in Japanese Patent Application Laid-open No. 2008-228360. The technique disclosed in Japanese Patent Application Laid-open No. 2008-228360 has a problem in that estimated friction is limited to linear friction and that nonlinear friction cannot be estimated.